Maybe someone can help me understand this. i guess it applies to any engine, stock or swapped.
There is a warning light on the fiero dash that comes ON when the alternator stops charging. If this light bulb is burnt out, the alternator will NOT charge and the battery goes dead. If the wiring in this circuit is broken, the alternator doesn't charge and the battery goes dead.
Is this a direct connection to the alternator or does it go to the ECM and the ECM tells the alternator to stop charging ?
Is there a "work-around" to hardwire the alternator into thinking this light is always working, such as grounding the "control" wire ?
I'm asking for a friend and myself. On several fieros I've had, including my 3800SC, I've had problems with this.
Maybe someone has a wiring diagram (?)
Thank you.
[This message has been edited by PaulJK (edited 08-10-2014).]
This only applies to the non-ecm controlled CS series alternators, as I recall. The alternator is expecting to see a small amount of resistance back to switched B+ on one of the control circuits (I don't recall which at the moment). You can wire a resistor between an ignition switched source to bypass the charging light. Or there are SI to CS adapter harness with it built in. If you look into CS conversions for vehices without factory charge lights you can read all about it. The forums at ColoradoK5 have some good info.
[This message has been edited by FieroJimmy (edited 08-10-2014).]
The alternator plug must have 12v constant (battery) on terminal A (red). This is supplied from the battery junction terminal below the c500. Plug terminal B (brown) is 12v ignition and is supplied from that GAGE fuse power routed thru the charge indicator light. Both voltages must be present for the alternator to charge. Because 12v is on both sides of the bulb when the alternator is charging, the bulb does not light. If the alternator quits charging, the bulb lights due to power flowing from the GAGE fuse to the alternator.
If SI then need the light circuit to turn on the alt. If CS type... See my Cave, CS Alternator
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
You just need to wire in a 50ohm resitor in parallel to the light so in case it goes out the alt still charges.
If the light comes on when the engine is running, either the alternator is failing/has failed or the battery voltage is dropping. Try revving the engine and: ◦If the lamp gets brighter, suspect a bad battery ◦If the lamp gets dimmer, suspect a bad alternator
i have a 87 fiero 2.8 auto , someone tied into the red wire next to the battery and ran it up to the key switch and if i unhook it the light on the alt gage will come on , not had time to trouble shoot it yet , working on other things , hope this helps
This is a common thing. I have another car MGB that does the exact same thing. The light adds a small resistor to the circuit and cause a current to flow to the alternator which creates a magnetic field for the alternator. Some alternator are self actuating and this resistance is not needed. Sometimes an alternator will have enough residual magnetic field that it will work without the light but the magnetic field can fade with time. The easiest way to fix it is to replace the light bulb. Putting a resistor in parallel will also fix it but it seems to be extra work.
I don't quite understand how the alternator doesn't charge without the battery light on the dash. I removed my aux gauge pod a while back and have not had any real charging issues. Mine is a 1986 though?
------------------ My Fiero: 1986 Pontiac Fiero GT, V6, 4-speed manual
This is probably useless theorizing, but I'm wondering about the effects of adding a parallel circuit for the warning lamp because these are the things that keep me up at night, or more specifically the possible adverse effects. I'm not an electrical engineer, but at the risk of sounding like an idiot this is what I've put together in my head.
In theory, adding a parallel circuit for the warning lamp reduces the resistance of the circuit to the field current supply. The effects of this are that (theoretically) voltage remains the same but current increases. So, (in theory), adding a parallel circuit for the warning lamp can reduce overall resistance of the field supply circuit and increase current. This can increase the electromagnetic field and in turn increase alternator output (before the voltage regulator) which can (theoretically) increase heat generation which at a certain level can be a problem.
Now, realistically, here is what I expect is more true. I'm not sure what the usual resistance of the warning lamp circuit is, but 50 ohms is probably quite a bit more than normal. From what I can see with a quick google search, the usual field resistance of the alternator is around 5 ohms but can vary. As such, I expect that the relative decrease in resistance and increase in current is relatively small. I'm not sure where the 50 ohm recommendation came from but I'm guessing it's sufficiently high enough to not allow a significant increase in current. Furthermore, once running, the alternator is self-exciting and this circuit is playing a negligible role in alternator function compared to the role of the voltage regulator.
Of course. Not genuinely concerned in the least, just like to understand the effects of making changes to pre-existing circuits even though I know it's "okay". I like to understand how things work, how the size of a resistor is chosen in a situation like this, and also have a better idea of when things aren't going to work.
For example, what if you used a 1 ohm resistor instead? No resistor? I used the word theoretically a lot for a reason. It's meant to be an academic question for sure, even though its coming from somebody who's academics are in a different field despite having wired a large number of combination circuits before.
But hey, maybe I'm the only one.
EDIT: Edit to say that its a no-brainer that a resistor is typically chosen based upon the voltage of the system and the desired current, which is usually kept within a range that will avoid overheating the wiring or damaging sensitive devices if there are any. What I felt made this question interesting is the alternator, as a small change in field current can produce a significantly larger increase in output. I still don't think its a concern here, but that's what I thought would be interesting to discuss.
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Originally posted by olejoedad:
Parallel circuits containing a resistor are very common.
[This message has been edited by GraterFang (edited 06-09-2023).]
The Dash Light has Nothing to do w/ alt's coils in GM or other brands of vehicles.
Power Generated by the Alt is a function of coil winding plan and more but Not that light.
It just used by the Regulator to try to warn you and turn on when start the car. Note that Some alts delay turn On a bit so don't think all vehicles will have 14-15v instantly using dash meter or any other meter.
Many vehicles have a light. Some don't like 84 Fiero but somewhere in the harness has ~ 10Ω resistive wire (for GM. Others may charge &ohm and very hard to see w/o tearing harness cover off. When a vehicle have Volt and/or amp meter is not = to the light/resistor as far as the alt sees.
⚠️ Warning: If put 2 resistor in parallel will cut Ω and can kill the Regulator. Only when the OEM light/resistor doesn't seem work... you discon the OEM part in one of a few ways like for most Fiero, unplug the light in the dash. Then use a test light from battery to lamp pin on the alt.
OEM light bulb maybe 100% Good but wires to it goes thru many other places/plugs and maybe one area is bad. Quick Jump w/ Test Light bypass all of that. But if made such a thing, type of lamp matters. 194 and related are ok but not a brake light or others eating 1 or more amps.
The Dash Light has Nothing to do w/ alt's coils in GM or other brands of vehicles.
Power Generated by the Alt is a function of coil winding plan and more but Not that light.
It just used by the Regulator to try to warn you and turn on when start the car. Note that Some alts delay turn On a bit so don't think all vehicles will have 14-15v instantly using dash meter or any other meter.
Ogre, you probably know better than me but this doesn't fit with my understanding of how this works. My understanding is that the 12+V that runs through the warning lamp is used to excite the coils in the alternator (even if going through the voltage regulator first). Once functioning, the alternator provides this voltage itself and is self sustaining. At the same time, the 12+V the alternator is producing for this purpose negates the voltage difference which is why the warning lamp is no longer lit.
As supporting evidence, here is quote from the link provided above by sardonyx247
quote
The regulator uses transistors to control the field current. A transistor is a device used to amplify and switch electronic signals. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current flowing through another pair of terminals. When system demand causes a voltage drop (the control voltage inputis less than nominal) the regulator senses this and a small current is sent to a transistor which amplifies it and sends it to another transistor which acts as a valve in controlling the flow of the field current input to the rotor.
The field current supply is provided from one of two different sources, depending on the state of the alternator. When the engine is not running and the alternator is not spinning and producing electricity, the field current supply comes from the vehicle's battery, via the ignition switch and alternator warning lamp (if equipped). We'll go into more detail on the warning lamp shortly. The process of supplying battery voltage to "kick-start" or "prime" the alternator is known as "exciting" the alternator, and the wire that carries the current from the alternator warning lamp to the appropriate voltage regulator terminal is known as the "exciter" wire. A few special alternators do not have this wire and are known as "self-exciting"- we'll cover this in more detail in the wiring section.
After the engine is started, and the alternator is generating electricity the diode trio feeds the alternator output back to the voltage regulator to serve as the field current supply.
Theoretically, once up to speed, the alternator is self sustaining, and the car will run without a battery until it is shut off (as long as system demand does not exceed alternator output capacity). However - you should never disconnect the battery in a running vehicle as doing so can cause voltage surges that can damage not only the voltage regulator, but also other on-board electrical equipment - particularly computer-controlled devices. Remember the diagram of the pulsed DC output from the alternator and the fact that the battery acts as a large filter or cushion in the system.
Note that the field current is much smaller than the output current produced in the stator windings. For example, to produce 70 amperes of DC, the field current required will be less than 2 amperes.
So, you're saying that the 12+V through the warning lamp is NOT used for excitation? And if so, what is occurring exactly then that prevents the alternator from functioning when this circuit has a disconnect?
quote
⚠️ Warning: If put 2 resistor in parallel will cut Ω and can kill the Regulator. Only when the OEM light/resistor doesn't seem work... you discon the OEM part in one of a few ways like for most Fiero, unplug the light in the dash. Then use a test light from battery to lamp pin on the alt.
I'd appreciate more information on this is as well. Are you saying that wiring in a 50 ohm resistor in a parallel with the warning lamp (if equipped -- a resistor if not) as suggested above will indeed potentially cause harm to the alternator? Is this due to an increase in current as I suggested above, and if not what is the cause? An increase in current from a parallel 50 ohm resistor should be fairly minimal (unless being amplified by the alternator due to an increase in field current). If this is what you're stating, then there is some conflicting information here that should be clarified so that people aren't making harmful changes to their electrical system.
[This message has been edited by GraterFang (edited 06-09-2023).]
This may sound off topic but I used my spare alternator on our forklift and it does not have an idiot light, only an ammeter. It has been charging just fine for several years now. I think we are all trying to make this too complicated. sorry I had to get a part number .what we used to make it all work was get a painless performance #30706 resistor plug assembly from Summit to eliminate the light circuit. What I don't understand is why you would want to eliminate the dash light on your car?
[This message has been edited by sleek fiero (edited 06-09-2023).]
This may sound off topic but I used my spare alternator on our forklift and it does not have an idiot light, only an ammeter. It has been charging just fine for several years now... what we used to make it all work was get a painless performance #30706 resistor plug assembly from Summit to eliminate the light circuit.
I think as long as the appropriate circuits are complete, the alternator will work regardless of whether or not a light is present. The light is in essence simply a resistor that lights up. There is a possibility that having the wrong resistance/current could affect the quality or longevity of the alternator's function, though, which is what I was trying to start a discussion over.
quote
Originally posted by sleek fiero:
I think we are all trying to make this too complicated.... What I don't understand is why you would want to eliminate the dash light on your car?
I certainly wouldn't, but some might. What's more likely from this thread though is that somebody might add a "backup" parallel circuit as described above so that the alternator continues to function even if the warning light goes out or if some other problem with the circuit occurs. However, if having the wrong current to the voltage regulator is harmful I think some of us would want to know that.
Personally, I just want to know because I want to know. I enjoy the details.
[This message has been edited by GraterFang (edited 06-10-2023).]
and very hard to see w/o tearing harness cover off.
